Debugging FCode ROM

[BALATON Zoltan]

Hello,

I'm trying to find out what's missing to use an FCode ROM for the ati-vga 
device to see how it would set up the card for MacOS. This has been done 
before for other FCode ROMs e.g. here:

https://mail.coreboot.org/hyperkitty/list/[e-mail]/thread/E7PFX...

I can get some print out of compiling and defining new words by setting 
fcode-debug? and ?fcode-verbose to true as above but this only gives me 
what I can also get from detok but does not tell me where exactly it fails 
during executing these words afterwards. What I get is that after a lot of 
(compile), new-token and fcode# lines that define a lot of words it just 
ends in one of these (the second?) when executed:

400514a :  [ 0x8bc ]
400514c :  [ 0x926 ]

byte-load: exception caught!

But how can I see what's inside this word that caused the exception? 
There's the forth debugger I think to see or step through execution of 
words but how can I add an undefined/unnamed word to the debug before the 
the FCode runs?

Looking at the definition of this word in the detok output does not get me 
further as it just calls more of these words defined in the FCode:

8512: b(:)
   8513:     (unnamed-fcode) [0x86a]
   8515:     (unnamed-fcode) [0x864]
   8517:     b(") ( len=7 )
             " map-out"
   8526:     (unnamed-fcode) [0x91f]
   8528:     (unnamed-fcode) [0x86c]
   8530:     (unnamed-fcode) [0x866]
   8532:     b(") ( len=7 )
             " map-out"
   8541:     (unnamed-fcode) [0x91f]
   8543:     0
   8544:     b(to) (unnamed-fcode) [0x86c]
   8547:     0
   8548:     b(to) (unnamed-fcode) [0x86a]
   8551: b(;)
   8552: new-token 0x926

so where can I get more details on execution of these words and the more 
precise location of the exception?

Regards,
BALATON Zoltan